1. Field of the Invention
The present invention relates to an electron source and an image-forming apparatus, such as a display device, using the electron source, and more particularly to an electron source comprising a number of surface conduction electron-emitting elements and an image-forming apparatus using the electron source.
2. Related Background Art
Heretofore, two types of electron-emitting elements are known; i.e., a thermal electron source and a cold cathode electron source. Cold cathode electron sources include electron-emitting elements of field emission type (hereinafter abbreviated to FE type), metal/insulating layer/metal type (hereinafter abbreviated to MIM type), and surface conduction type, etc. Examples of FE type elements are described in, e.g., W. P. Dyke & W. W. Dolan, "Field emission", Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, "PHYSICAL Properties of thin-film field emission cathodes with molybednum cones", J. Appl. Phys., 47, 5248 (1976).
One example of MIM type elements is described in, e.g., C. A. Mead, "The tunnel-emission amplifier", J. Appl. Phys., 32, 646 (1961).
One example of surface conduction electron-emitting elements is described in, e.g., M. I. Elinson, Radio Eng. Electron Phys., 10, (1965).
A surface conduction electron-emitting element utilizes a phenomenon that when a thin film having a small area is formed on a substrate and a current is supplied to flow parallel to the film surface, electrons are emitted therefrom. As to such a surface conduction electron-emitting element, there have been reported, for example, one using a thin film of SnO.sub.2 by Elinson as cited above, one using an Au thin film [G. Dittmer: "Thin Solid Films", 9, 317 (1972)], one using a thin film of In.sub.2 O.sub.3 /SnO.sub.2 [M. Hartwell and C. G. Fonstad: "IEEE Trans. ED Conf.", 519 (1975)], and one using a carbon film [Hisashi Araki et. al.: "Vacuum", Vol. 26, No. 1, p. 22 (1983)].
As a typical configuration of those surface conduction electron-emitting elements, FIG. 19 shows the element configuration proposed by M. Hartwell in the above-cited paper. In FIG. 19, denoted by reference numeral 101 is an insulating substrate. 102 is a thin film for forming an electron-emitting region which comprises, e.g., a metal oxide thin film formed by sputtering into an H-shaped pattern. An electron-emitting region 103 is formed by the energizing process called forming (described later). 104 is a thin film including the electron-emitting region 103. The dimensions indicated by L1 and W in the figure are set to 0.5-1 mm and 0.1 mm, respectively.
In those surface conduction electron-emitting elements, it has heretofore been general that the electron-emitting region forming thin film 102 is subjected to the energizing process called forming in advance to form the electron-emitting region 103 before starting emission of electrons. The term "forming" means the process of applying a voltage across the electron-emitting region forming thin film 102 to locally destroy, deform or denature it to thereby form the electron-emitting region 103 which has been transformed into an electrically high-resistance state. The electron-emitting region 103 emits electrons from the vicinity of a crack generated in a portion of the electron-emitting region forming thin film 102. The electron-emitting region forming thin film 102 including the electron-emitting region 103 which has been formed by the forming process will be referred to here as the electron-emitting region including thin film 104. In the surface conduction electron-emitting element after the forming process, a voltage is applied to the electron-emitting region including thin film 104 to supply the element with a current, whereupon electrons are emitted from the electron-emitting region 103.
The above surface conduction electron-emitting element is simple in structure and easy to manufacture, and hence has an advantage that a number of elements can be formed into an array having a large area. Therefore, various applications making use of such an advantage have been studied. Examples of the applications are a charged beam source and a display device. As an example in which a number of surface conduction electron-emitting elements are formed into an array, there is proposed an electron source that surface conduction electron-emitting elements are arranged in parallel, ends of the elements are interconnected by respective leads for each of opposite sides to form one row of an array, and a number of rows are arranged to form the array (See, e.g., Japanese Patent Application Laid-Open No. 64-31332 by the applicant). In the field of image display devices or the like, particularly, flat display devices using liquid crystals have recently become popular instead of CRTs, but they are not self-luminous and have a problem of requiring backlights. Development of self-luminous display devices have therefore been desired.
An image display device in which an electron source having an array of numerous surface conduction electron-emitting elements and a fluorescent substance radiating visible light upon impingement of electrons emitted from the electron source are combined with each other to form a display device, is a self-luminous display device which is relatively easy to manufacture and has good display quality while providing a large screen size (See, e.g., U.S. Pat. No. 5,066,883 by the applicant).
In the above self-luminous display device with an electron source using surface conduction electron-emitting elements, a desired one of the numerous surface conduction electron-emitting elements making up the electron source, which is to emit electrons for radiating light from the fluorescent substance, is selected by combination of a linear electron source (referred to as a row-direction electron source) comprising the numerous surface conduction electron-emitting elements which are arranged in parallel to lie in the row direction (or called X-direction) and interconnected by leads, and a drive signal applied to corresponding one of control electrodes (called grids), which are disposed in spaces between the electron source and the fluorescent substance, in a direction (called column direction or Y-direction) perpendicular to the row-direction electron source (See, e.g., Japanese Patent Application Laid-Open No. 64-31332 by the applicant).
In that image display device, it is naturally required to produce a good image with less variations in specific properties such as brightness that not only horizontal alignment between the individual surface conduction electron-emitting elements and the corresponding grids, but also vertical distances between the grids and the surface conduction electron-emitting elements are uniform. Therefore, the applicant has proposed a novel structure that grids are laminated over surface conduction electron-emitting elements, which is effective to align the grids and the surface conduction electron-emitting elements with high accuracy (See, e.g., Japanese Patent Application Laid-Open No. 3-20941 by the applicant).
In a conventional electron source having grids and an image display device having such an electron source, it is generally possible to control convergence and divergence of electron beams by properly controlling a voltage applied to the grids.
In the image display device, proposed by the applicant, wherein numerous surface conduction electron-emitting elements are arrayed to form an electron source and a fluorescent substance is disposed in opposite relation to the electron source, grids disposed to lie in a direction (column direction) perpendicular to leads (row-direction leads) for the elements arranged in parallel have also been indispensable to select the desired element for emitting electrons.
Further, in order that the fluorescent substance disposed in opposite relation to the electron source radiates light with brightness selectively controlled, the grids disposed to lie in the direction perpendicular to the row-direction leads for the elements have also been indispensable.